Flat-flame gas burner

ABSTRACT

A fuel gas burner adapted for mounting in a heat treating furnace and for generating a relatively large expanse of radiant energy toward an object to be heated or heat treated. The burner has a housing with separate inlets for fuel gas and air and an air plenum with a forwardly facing throat. Surrounding the plenum throat is a combustion block formed of refractory material shaped to define a forwardly-facing frusto-conical heat radiating surface. A central fuel gas supply tube coaxial with the plenum throat has a nozzle element and a cooperating distributor mounted on its forward end to define with the plenum throat an annular air passage and a fuel gas chamber communicating with the supply tube. The nozzle element has radially extending circumferential vanes that define with the plenum throat, swirl producing slots adapted to receive air from the plenum chamber through the annular passage and fuel gas through ports communicating with the fuel gas chamber. The resulting fuel-air mixture which has a swirling motion imparted by the slots is ignited and propelled radially outward against the frusto-conical surface of the combustion block to produce a generally flat-flame. This produces a relatively large expanse of heat radiation directed toward the area to be heated.

BACKGROUND OF THE INVENTION

This invention relates to direct-fired fuel gas heating or heat treatingfurnaces such as for annealing steel strip and especially to a burneradapted for mounting in the furnace wall for mixing and igniting fuelgas and air and for producing a swirl effect in the combustion zone thatresults in a flat-flame pattern. More particularly, the inventionrelates to direct-fired fuel gas burner construction that produces agenerally flat-flame to generate a large expanse of heat radiation.

Flat-flame burners of the general type to which the present invention isdirected are adapted to impart a swirling movement to a mixture of fuel,gas and air so that when ejected from the nozzle, the mixture and flameflares outwardly. As a result, the swirling gaseous mixture progressesfrom the nozzle at a relatively low forward velocity but with arelatively larger tangential velocity. Thus, the flame spreads outwardlyin radial fashion and tends to remain close to the surface of thecombustion block.

The result of the general construction described above is a wide, flatexpanse of flame with sufficient turbulence for intimate mixing of fuel,gas and air and complete combustion. The combustion takes place largelyin a radially extending path rather than in an axial path so that theflame extends over a wide area.

SUMMARY OF THE INVENTION

It is among the objects of the invention to produce an improvedflat-flame fuel gas burner which provides an advantageous flame patternand high heating efficiency and which may be readily modified to providea wide range of heat output capability.

Another object of the invention is to produce a direct-fired flat-flamefuel gas burner of a less complicated construction and at a reducedcost.

A further object of the invention is to produce a flat-flame burnerwhich can readily be modified to accommodate different gaseous fuelsand/or to increase or decrease the burner capacity, i.e., output inB.T.U.'s per hour.

These and other objects and advantages are achieved with the novelburner construction of the invention which comprises a housing adaptedto be supported by a sidewall of the heat treating furnace in which itis to be used and which defines an air plenum communicating with an airinlet preferably connected to a conduit that passes through theinsulated wall of the furnace. The housing also has a forwardly facingcylindrical plenum throat. Surrounding the plenum throat and spacedforwardly therefrom to define a circular shoulder is a combustion blockformed of refractory material and having a generally frusto-conicalsurface facing generally in the direction of the interior of thefurnace. Extending through the housing is a fuel gas supply tube that iscoaxial with the plenum throat and which supports a nozzle element and adistributor. The distributor extends radially outward toward the plenumthroat to define therewith a relatively thin annular air passage.

The nozzle element has radially extending circumferentially inclinedvanes that define, with the forward portion of the distributor, swirlproducing slots which are adapted to receive air from the plenum throughan annular air passage. The distributor and nozzle element definetherebetween a fuel gas chamber that receives fuel gas through a supplytube and ports are provided between the slots and the chamber forintroducing fuel gas from the supply tube into the slots in the nozzleto be mixed with air. The slots impart an angular velocity or swirl tothe fuel-air mixture so that when the mixture exits the slots and isignited it progresses radially outward with a spiral or swirling motionso that a large flat-flame is formed closely adjacent the frusto-conicalsurface of the combustion block.

The arrangement of the plenum throat, the distributor and the nozzleelement is such that by readily effected modifications, which will belater described, the burner can be adapted for different gaseous fuels,such as natural gas, coke oven gas or butane, and the burner capacity oroutput may be increased or decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central sectional view illustrating a heat treating furnacefor annealing strip steel in coil form and including direct-firedflat-flame burner units embodying the present invention;

FIG. 2 is a fragmentary broken sectional view on an enlarged scaleillustrating in more detail a portion of the heat treating furnace ofFIG. 1;

FIG. 3 is a fragmentary sectional view on a still larger scale taken online 3--3 of FIG. 4 and illustrating a flat-flame burner embodying theinvention and of the type shown in FIGS. 1 and 2;

FIG. 4 is a front elevational view taken substantially on line 4--4 ofFIG. 3;

FIG. 5 is a side elevational view with parts broken away better toillustrate the nozzle element and distributor of the flat-flame gasburner of FIGS. 3 and 4;

FIG. 6 is a fragmentary sectional view taken on the line 6--6 of FIG. 5;and

FIG. 7 is a front elevational view, with parts broken away, taken on theline 7--7 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings and initially to FIGS. 1 and2, there is shown a bell type annealing furnace 10 such as isextensively used for annealing coils 11 of strip steel. The furnace hasan insulated cylindrical sidewall 12 and an insulated top 13 to definetherein a heating chamber 14. Located within the heating chamber 14 is aremovable inner cover 15 adapted to have a gas tight seal with the floorof the furnace to permit the introduction and maintenance of an inertgas atmosphere to prevent the adverse effects of oxidation during theannealing process.

In order to generate the heat required for the annealing operation, aplurality of flat-flame burner units 20 are mounted in circumferentiallyspaced relation in the cylindrical sidewall 12 of the furnace bell 10.The heat from these burners is effective directly against the outer wallof the inner cover 15. Surrounding the cylindrical furnace wall 12 is anannular fuel gas supply manifold 21 with spaced supply lines 22 forfeeding fuel gas to the individual burner units 20.

Located near the upper portion of the furnace wall 12 is an annular airmanifold 23 which supplies combustion air. For each of the burners,there is an air inlet pipe 24 connected to a recuperator 25 whichextends through an exhaust passage 26 formed in the upper portion of thefurnace wall 12. These passages 26 provide outlets for the products ofcombustion from the burners 20 which products enter the heating passages26 through radial ports 27 in the furnace wall 12 and exit throughopenings at the upper end of the furnace. The gaseous combustionproducts as they move through the passages 26 heat the recuperators 25and the combustion air passing therethrough. The preheated combustionair is then passed through the lower sections 28 of the air inlet tubeswhich extend downwardly to their respective burner unit 20. Each lowersection 28 preferably has an expansion section 29 at the lower end toaccommodate expansion and contraction caused by heating and coolingduring the heat treating operation.

Referring now to FIGS. 3 to 7, each burner unit 20 has a rectangularhousing 30 which includes a rear wall 31, top and bottom walls 32 and33, sidewalls 34 and 35, a front wall 36 and two parallel verticalpartition walls 37 and 38 positioned between the front wall 36 and rearwall 31. The front wall 36 has a cylindrical nozzle throat 39 extendingforwardly therefrom to receive the various nozzle components to bedescribed in more detail later. The front wall 36 is spaced behind thefront edges of the top, bottom and side walls 32, 33, 34 and 35 so as todefine therewith a rectangular recess 40 adapted to receive a refractoryblock 41 having a central circular opening 42 that fits around thecylindrical nozzle throat 39. It will be understood that the housingmay, if desired, be cast rather than fabricated as illustrated in thedrawings.

The refractory block 41 has a forwardly facing frusto-conical surface 43and a circular recess forming a combustion ledge 44 concentric with thecentral opening 42 and defining, with the frusto-conical surface 43, anannular shoulder 45. The recess or ledge 44 extends into the path of thefuel-air mixture as it is discharged from the nozzle assembly and isvery effective in the final mixing of the fuel-air mixture. The coneangle of the frusto-conical surface 43 is large enough that theflat-flame does not impinge thereon. This permits the flame to reach thelargest possible diameter before completion of combustion. Also thisminimizes the possibility of an undesirable hot spot effect on the wallof the inner cover 15.

The vertical partition walls 37 and 38 define with the top and bottomwalls 32 and 33 and the front and rear walls 36 and 31, an air plenum 46communicating with the nozzle throat 39. Air enters the air plenum 46through an opening 47 in the top wall 32. An air inlet sleeve 48 extendsfrom the top wall 32 around the opening 47 and provides a fitting toreceive the lower section 28 of the air supply pipe 24 as bestillustrated in FIG. 3. It will be understood that in some cases the airinlet to the plenum 46 may be modified as by locating it through therear wall 31 or other convenient location.

Referring again to FIG. 3, it will be noted that the burner housing 30is secured in the side wall of the furnace 10 by means of threadedmounting studs 51, 52 and 53. The housing 30 is spaced inwardly from theoutside of the furnace wall 12 by means of spacer sleeves 54, 55 and 56through which the mounting studs 51, 52 and 53 extend. The studs aresecured to the wall 12 by nuts 57. This arrangement eliminatessupporting the housing 30 on the refractory material of the furnacewall, thus facilitating the use of ceramic fiber insulation as theinsulating material.

The refractory block 41 is retained in the housing 30 by a fasteningarrangement including a groove 58 in the vertical sidewalls of the block41 to provide a seat for key elements that are inserted through anelongated hole 59 formed in the walls 32 and 33. The keys are locked inplace when the housing is positioned in the rectangular seat formed inthe furnace wall 12.

A fuel gas inlet tube 60 extends through the housing 30 and ispositioned within a guide sleeve 61 welded to and extending through therear wall 31. The inlet tube 60 is adjustably locked to the sleeve withset screws 62 and has a threaded forward end adapted to receive a nozzlemember 63 having a sleeve portion 64 with internal threads. On its outersurface the sleeve portion 64 receives a cup-shaped distributor 65 whichis secured thereon as by the set screw 66. The distributor 65 has acurved radial flange portion 67 (see FIG. 5) that extends radiallyoutward almost to the inner surface of the nozzle throat 39 to definewith the throat an annular air passage 68 communicating with the airplenum 46. The distributor 65 also has an annular return flange 69 (seeFIG. 6) against which the nozzle element 63 rests. The distributor 65defines with the rearward face of the nozzle element 63 an annularfuel-gas chamber 70 into which fuel-gas is introduced from the inlettube 60 through radial ports 71 formed in the sleeve portion 64 of thenozzle element 63. The nozzle element 63 has a plurality of radiallyextending helical vanes 73 and 74 that define therebetween swirlproducing slots 75 (see FIGS. 5 and 7). Air enters each of the slots 75through the annular passage 68 (FIGS. 3 and 6) while fuel gas enterseach of the slots 75 through the ports 76 formed in the return flange 69of the distributor 65.

The shape of the vanes 73 and 74 is illustrated in FIG. 5 and it will benoted that the air and gas which enter the slots 75 between the vanes 73and 74 has a helical motion imparted thereto to develop a swirling andmixing effect as the gas and air move outward from the slots.

The three vanes 73 have a radial dimension slightly greater than theother vanes 74 so that the vanes 73 seat snugly within the plenum throat39. With this construction, only the three vanes 73 need be accuratelymachined to provide a snug fit in the plenum throat 39, thus eliminatingthe necessity of machining the outer ends of the other vanes 74. Thefuel gas and air that enter a slot 75 immediately begin to intermix toform a fuel-air mixture suitable for combustion. As the resultingmixture exits the slots 75 with a swirling motion, it is ignited usingone or more ignitor plugs 80 mounted in tubes 81 (see FIGS. 3 and 4)that extend through the front and rear walls 36 and 31 respectively ofthe housing 30 and into the combustion zone forwardly of the nozzleassembly. The illustrated construction, including the combustion ledge44, produces a flat-flame pattern that is closely adjacent thefrusto-conical face 43 of the refractory block 41 and thus each burnerheats a wide expanse of the inner cover 15.

Generally speaking, for a given burner capacity, a fixed quantity ofcombustion air is required regardless of the type of gaseous fuelutilized. The outside diameter of the distributor 65 can thus be fixedas related to a given burner capacity. Within this given burnercapacity, alternate fuels can be utilized by providing a particulardiameter for the several gas ports 76 in the distributor itself. Forexample, natural gas will require one diameter; and the use of coke ovengas, which has less B.T.U.'s per standard cubic foot, will require alarger gas port diameter for the same B.T.U.'s per hour. Similarly, theuse of a propane gas, which has more B.T.U.'s per cubic foot thannatural gas, will require a smaller gas port diameter. Thus, for a fixedburner capacity, the outside diameter of the distributor 65 would remainthe same and alternate gaseous fuels could be accommodated by changingonly the diameter of the several gas ports 76.

The burner capacity in B.T.U.'s per hour can be changed by increasing ordecreasing the outside diameter of the distributor 65 and by aconcurrent change in the diameter of the gas ports 76. For example, toincrease the burner capacity, the outside diameter of the distributor 65would be reduced to provide a greater area of the annular passage 68through which the combustion air flows. With this increased aircapacity, the diameter of the several gas ports 76 would beproportionally increased. Similarly, to decrease the burner capacity,the outside diameter of the distributor 65 would be increased and thediameter of the gas ports 76 would be decreased. From the above, it willbe understood that changes of substantial degree can be made in theburner capacity, and concurrent or independent changes in type of fuelcan be accommodated, by simple and inexpensive changes in the outsidediameter of the distributor 65 and/or the size of the gas ports 76 inthe distributor.

Further in view of the unique construction of the nozzle assembly it ispossible to achieve a desired fuel-air mixture for optimum combustionthrough a wide range of fuel gas pressures and thus the burner unit 20may be operated with optimum efficiency even though fuel gas pressurevaries considerably.

While the invention has been shown and described with respect to apreferred embodiment thereof, this is intended for the purpose ofillustration rather than limitation and variations and modifications ofthe specific construction herein shown and described will be apparent tothose skilled in the art, all within the intended spirit and scope ofthe invention. Accordingly, the patent is not to be limited in scope andeffect to the specific embodiment herein shown and described nor in anyother way that is inconsistent with the extent to which the progress inthe art has been advanced by the invention.

I claim:
 1. A fuel gas burner adapted for mounting in a furnace wall facing the interior of the furnace and comprising:an air inlet tube connected to said housing and having a section thereof extending through a portion of the wall of said furnace to heat air passing therethrough, a housing defining an air plenum communicating with said air inlet, and also defining a forwardly facing plenum throat, a combustion block formed of refractory material mounted in said housing surrounding said plenum throat and having a generally frusto-conical surface, a fuel gas supply tube extending into said plenum throat, distributor means mounted at the inner end of said supply tube and extending radially outward toward said plenum throat and defining therewith an annular air passage communicating with said plenum, a nozzle element mounted at the inner end of said gas supply tube and defining with said distributor means a fuel gas chamber communicating with and located around said gas supply tube, said nozzle element having radially extending, pitched circumferential vanes that define swirl producing slots adapted to receive air from said plenum through said annular passage, means for introducing fuel gas from said fuel gas chamber into said slots to be mixed with air, and means for igniting the resulting fuel-air mixture to produce a generally flat-flame extending radially outwardly adjacent said frusto-conical surface.
 2. A fuel gas burner adapted for mounting in a furnace wall facing the interior of the furnace and comprising:a housing defining an air plenum communicating with an air inlet, and also defining a forwardly facing plenum throat, a combustion block formed of refractory material mounted in said housing surrounding said plenum throat and having a generally frusto-conical surface, a fuel gas supply tube extending into said plenum throat, an annular distributor mounted at the inner end of said supply tube and having a radial flange extending outward toward said plenum throat to define therewith an annular air passage communicating with said plenum, and also having a radial return flange spaced forwardly from said first named flange, a nozzle element mounted at the inner end of said gas supply tube and seated against said radial return flange to define with said distributor means a fuel gas chamber communicating with and located around said gas supply tube, said nozzle element having radially extending, pitched circumferential vanes that define swirl producing slots adapted to receive air from said plenum through said annular passage, means for introducing fuel gas from said fuel gas chamber into said slots to be mixed with air, and means for igniting the resulting fuel-air mixture to produce a generally flat-flame extending radially outwardly adjacent said frusto-conical surface.
 3. A fuel gas burner as defined in claim 2 wherein said return flange has a plurality of circumferentially spaced ports formed therein and communicating with said slots.
 4. A fuel gas burner as defined in claim 3 wherein one port is provided for each slot.
 5. A fuel gas burner as defined in claim 2 wherein said combustion block has a central opening formed therein and through which said plenum throat extends and a concentric circular recess formed in the forward face of said block to define a combustion ledge located generally in the path of the fuel-air mixture projected from said slots. 